There are 3 barriers to study-and when you run into one they have physical manifestations. The first barrier is going past a word that you don't understand, it can be having the wrong definitions or no definition, misunderstanding can occur in a number of ways. When our daughter came home from school and was unhappy or less than just happy we'd ask- was there a word that you didn't understand- often she would just tell us. If she didn't know right away then we'd ask what she'd studied during the day, and go over that and find something she had mis understood. As soon as we cleared the word she would brighten up. And be happy about going to school again, too by the way.
There are 2 other barriers to study we also used. These barriers were discovered by L Ron Hubbard. There is a Learning center here in Clearwater that tutors children and families on these barriers. I am not sure what is available where you are but I bet that you could call the local church and they could tell you where you could, &/or your child could take a course to learn how to use these 3 barriers to make school fun again.
If the barriers are handled he'll stop this behaviour- that is what I saw with our children. Please don't let him end up on some drug because he has encountered a barrier to study.
Best,k
ps contact me if you'd like and I'll check with the local learning center for what is in your area